apoenzimat

Apoenzime (apoenzyme) refers to the protein portion of an enzyme that is inactive on its own. The apoenzyme lacks a necessary non-protein helper, known as a cofactor, which is required for catalytic activity. When the cofactor binds to the apoenzyme, the resulting active enzyme is called a holoenzyme.

Cofactors come in two broad classes: inorganic ions (such as zinc, magnesium, or iron) and organic molecules known as coenzymes (such as NAD+, FAD, or coenzyme A). Some cofactors are tightly bound and form prosthetic groups, remaining associated with the enzyme, while others bind reversibly during catalysis. The presence of the cofactor can influence the enzyme’s structure, help stabilize the active site, or participate directly in the chemical reaction.

In many cases, apoenzymes are synthesized as inactive precursors and require activation by binding of the cofactor. This examples include metalloenzymes, where a metal ion is essential for function, and many dehydrogenases that require NAD+ or NADP+. Not all enzymes require cofactors; some are functional as apoproteins only after post-translational modifications or proteolytic activation to form an active holoenzyme.

Clinical and nutritional relevance arises because deficiencies in vitamins or mineral cofactors can impair enzyme activity, leading to metabolic dysfunctions. Understanding apoenzymes helps explain how enzyme activity is regulated and how deficiencies or inhibitors can alter metabolic pathways.